This invention relates to communications systems and more particularly relates to a communication system for use in hazardous confined areas.
There exist several situations in which a worker must enter a confined space in order to perform some work. One example of such a work situation is in the airplane industry, where workers must climb inside the fuel tanks located in the wings of an aircraft in order to clean and seal the inside of the fuel tanks before they are filled with fuel. Generally, the solvents which are used in cleaning these fuel tanks give off fumes which are toxic in varying degrees.
State and federal governments are enacting strict safety codes dealing with work in hazardous areas in order to protect workers from potential or actual dangers. For example, a typical regulation dealing with a situation such as the hazardous job of cleaning out aircraft fuel tanks calls for a lifeline to be attached to the worker who is inside the fuel tank. The lifeline is then run outside the confined space and a second worker is assigned to tend the lifeline so that in case of trouble the second worker can pull the first worker out of the hazardous situation by means of the lifeline.
A system involving lifelines and tenders requires that an extra person be placed on the job and results in a sharp increase in costs and inefficient use of personnel. It is desirable, therefore, to provide some other means for keeping in touch with a worker in a hazardous work area that does not involve such inefficient and costly measures.
Several systems have been devised in the prior art for dealing with such situations. One such system is shown in U.S. Pat. No. 3,588,858 to Demuth. In the Demuth system, a safety alarm system becomes activated when the body of a worker assumes a position other than a normal working position. The activation is provided by means of a position-sensitive switch attached to a radio transmitter which broadcasts a signal depending upon the position of the person wearing the transmitter. For example, so long as the worker is standing upright, no alarm is transmitted, however, should something happen to cause the worker to lose consciousness and fall, the change in position of the worker to a substantially horizontal position would cause the position-sensitive switch to activate the transmitter and send an alarm which in turn would be monitored by other personnel who could send help to the scene. There are certain disadvantages to use of a position-sensitive switch activated transmitter. The most significant one is that such a system will not work in an area where the normal working position cannot be predicted. For example, during the operation of cleaning an aircraft fuel tank mentioned above, the worker may be in a standing position at one point, crouching at another, sitting, and possibly even kneeling or lying down during his efforts in cleaning the inside of the tank. Therefore a position-sensitive switch would not work since the worker could be in several different positions and still not be in any danger.
Systems have also been devised using vapor-sensitive switches which activate an alarm transmitter when the buildup of vapors within the space reaches a certain level. The problem with a system based on vapor concentration is that there are several different kinds of solvents and several different kinds of vapors used with varying degrees of toxicity and varying allowable concentrations so that the vapor sensing range of the switch would have to be adjusted each time a different solvent was used and possibly even between operations if one solvent was used initially and then a second solvent was used for a second cleaning, for example.
It is also possible to monitor the vital signs of the worker such as breathing rate, heart rate, blood pressure, pulse, however, the systems which are capable of monitoring vital signs are expensive and generally the probes which are attached to the worker to make such measurements are complicated and difficult to attach.
It is therefore an object of the present invention to provide a communication system that can be used by workers in hazardous areas to both automatically monitor their well-being during their exposure in the hazardous area and also to allow them to summon assistance from the outside if need be.
It is a further object of this invention to provide such a communication system in which an alarm is automatically activated after a certain period of time has elapsed if the worker has not checked in with a command station prior to the lapsing of that time.
It is a further object of this invention to provide such a communication system in which the worker is alerted of the pending expiration of the check-in time period to prevent false alarms from being sent.
It is another object of this invention to provide such a communication system which can be utilized in connection with several workers in several locations simultaneously.
It is another object of this invention to provide such a communications system that is relatively inexpensive to manufacture and operate and simple for the worker to use.